I finally got LA NOIRE running-ish and is playable but lags my guess is the video card because is a 8400gs however i seen people play this games with * Pentium D * but with better card and some max there memory

I really do not know why you are trying to make something work that simply won't. You can't just put a new graphics cards into a machine and expect to work or even play.

Your grasping at straws and that is more annoying than just listening to what people are telling you and boat anchor that thing or use it for what it is.. a outdated computer that won't play anything recent.

Well its an upgrade sure but really isnt worth the money investing in very old hardware. your still going to run into problems.

those cards are better yes. more so the 9600 assuming you have a pci-e socket and not still agp since i think those are still around that age of hardware. unless its 7600 that was.
someone can chime in there.

Are you really on a very very tight budget?

How much did you pay for the old computer you have and were you told that is was a good gaming computer ?

and on a budget that why i found them because this is my issues i got one games that give me a pain * la noire * i only found out the problem that plague this games since they lock at 30FPS thank you rockstar and there stupid moved